This invention relates to resinous binder compositions which are admixtures of polyols and isocyanate urethane polymers. These compositions may be cured by known urethane catalysts including a gaseous catalyst. In another aspect this invention relates to curable urethane binder compositions which are useful for binding particulate solids. In particular the invention relates to urethane binders of the no bake and of the cold box type, which utilize an isocyanato urethane polymer as an isocyanate reactant or component. The binders are capable of bonding sand or other foundry aggregate to form molds or cores for casting of metals, especially aluminum and other lightweight metals which are cast at relatively low temperature. The cores and molds made using these binders demonstrate superior collapsibility or shakeout when used at low casting temperatures.